Roman looks like a Greek accusative - it should be Romam. I would have ignored it as a typo, but you did it twice in this post.

pmda wrote:How do I say (using supine) I came to Rome to be heard by Marcus?

2. Roman veni ab Marco auditum. (?)

Is passive indicated by ablative 'ab...Marco' on its own..?

You can't. With an active verb of motion, it denotes the action that the subject will be doing, as the purpose of motion. With iri, it denotes what will happen to the subject, but with no indication of purpose. Those are the only two uses of the supine in -um.

Romam veni Marcum auditum - "I came to Rome in order to hear Marcus."

Aemilia putat Marcum a Iulio verberatum iri - "Aemilia thinks Marcus is about to be beaten by Julius."

Hm, I won't rule this out, but I would really have to see a Classical example to accept it. Romam veni me auditum - "I came to Rome to hear myself". It seems to me that a Marco would just confuse things.

"Mundus it se perditum" = does that mean // significatne "The world is going to destroy itself" or "The world is going to be destroyed"?

I would take it as "the world is going to destroy itself", but I'm open-minded. Where is that from?